Geared turbofan with three turbines all co-rotating

ABSTRACT

A gas turbine engine has a fan rotor, a first compressor rotor and a second compressor rotor. The second compressor rotor compresses air to a higher pressure than the first compressor rotor. A first turbine rotor drives the second compressor rotor and a second turbine rotor. The second turbine drives the compressor rotor. A fan drive turbine is positioned downstream of the second turbine rotor. The fan drive turbine drives the fan through a gear reduction. The first compressor rotor and second turbine rotor rotate as an intermediate speed spool. The second compressor rotor and first turbine rotor together as a high speed spool. The high speed spool, the intermediate speed spool, and the fan drive turbine configured to rotate in the same first direction.

BACKGROUND

This application relates to a gas turbine having three turbine sections,with one of the turbine sections driving a fan through a gear changemechanism.

Gas turbine engines are known, and typically include a compressorsection compressing air and delivering the compressed air into acombustion section. The air is mixed with fuel and combusted, and theproduct of that combustion passes downstream over turbine rotors.

In one known gas turbine engine architecture, there are two compressorrotors in the compressor section, and three turbine rotors in theturbine section. A highest pressure turbine rotates a highest pressurecompressor. An intermediate pressure turbine rotates a lower pressurecompressor, and a third turbine section is a fan drive turbine whichdrives the fan.

SUMMARY

In a featured embodiment, a gas turbine engine has a fan rotor, firstand second compressor rotors, with the second compressor rotor forcompressing air to a higher pressure than the first compressor rotor. Afirst turbine rotor is configured to drive the second compressor rotor.The second turbine will drive the first compressor rotor. A fan driveturbine is positioned downstream of the second turbine rotor, and willdrive the fan rotor through a gear reduction. The first compressor rotorand second turbine rotor will rotate as an intermediate speed spool. Thesecond compressor rotor and first turbine rotor will rotate together asa high speed spool. The high speed spool will rotate in the same firstdirection as the intermediate speed spool, and the fan drive turbine.

In another embodiment according to any of the previous embodiments, thefan rotor to be is driven by a gear reduction to rotate in a seconddirection.

In another embodiment according to any of the previous embodiments, apower density of the engine is greater than or equal to about 1.5lbs/in³, and less than or equal to about 5.5 lbf/in³.

In another embodiment according to any of the previous embodiments, thepower density is defined as a ratio of thrust produced by the engineexpressed in pounds force to a volume of a turbine section incorporatingeach of the first turbine rotor, second turbine rotor and fan driveturbine rotor, expressed in cubic inches.

In another embodiment according to any of the previous embodiments, theratio is greater than or equal to about 2.0.

In another embodiment according to any of the previous embodiments, theratio is greater than or equal to about 4.0.

In another embodiment according to any of the previous embodiments, thethrust is sea level take-off flat-rated static thrust.

In another embodiment according to any of the previous embodiments, thefan rotor delivers a portion of air into a bypass duct and into thefirst compressor rotor as core flow.

In another embodiment according to any of the previous embodiments, amid-turbine frame is positioned between the first and second turbinerotors.

In another embodiment according to any of the previous embodiments, avane is positioned between the mid-turbine frame and second turbinerotor.

In another embodiment according to any of the previous embodiments, avane is positioned between the second turbine rotor and fan driveturbine.

In another embodiment according to any of the previous embodiments, avane is positioned between the second turbine rotor and fan driveturbine.

In another embodiment according to any of the previous embodiments, amid-turbine frame is positioned between the first and second turbinerotors.

In another embodiment according to any of the previous embodiments, avane is positioned between the mid-turbine frame and second turbinerotor.

In another embodiment according to any of the previous embodiments, avane is positioned between the second turbine rotor and fan driveturbine.

In another embodiment according to any of the previous embodiments, avane is positioned between the second turbine rotor and fan driveturbine.

In another featured embodiment, a gas turbine engine has a fan rotor,first and second compressor rotors, with the second compressor rotor forcompressing air to a higher pressure than the first compressor rotor. Afirst turbine rotor will drive the second compressor rotor, and a secondturbine rotor, with the second turbine for driving the first compressorrotor. A fan drive turbine is positioned downstream of the secondturbine rotor. The fan drive turbine will drive the fan rotor through agear reduction. The first compressor rotor and second turbine rotor willrotate in the same first direction as an intermediate speed spool. Thesecond compressor rotor and first turbine rotor will rotate together asa high speed spool in the same first direction as the intermediate speedspool. The fan drive turbine rotates in the same first direction as theintermediate speed spool. The fan rotor is driven by the speed reductionto rotate in an opposed second direction. A power density of the engineis greater than or equal to about 1.5 lbf/in³, and less than or equal toabout 5.5 lbf/in³. The power density is defined as a ratio of thrustproduced by the engine expressed in pounds force to a volume of aturbine section incorporating each of the first turbine rotor, secondturbine rotor and fan driving turbine rotor, expressed in cubic inches.

In another embodiment according to any of the previous embodiments, theratio is greater than or equal to about 2.0.

In another embodiment according to any of the previous embodiments, theratio is greater than or equal to about 4.0.

In another embodiment according to any of the previous embodiments, thethrust is sea level take-off flat-rated static thrust.

These and other features of the invention would be better understoodfrom the following specifications and drawings, the following of whichis a brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a gas turbine engine.

FIG. 2 shows how a volume of the turbine section can be calculated.

DETAILED DESCRIPTION

A gas turbine engine 20 is illustrated in FIG. 1, and incorporates a fan22 driven through a gear reduction 24. The gear reduction 24 is drivenwith a low speed spool 25 by a fan/gear drive turbine (“FGDT”) 26. Airis delivered from the fan as bypass air B, and into a low pressurecompressor 30 as core air C. The air compressed by the low pressurecompressor 30 passes downstream into a high pressure compressor 36, andthen into a combustion section 28. From the combustion section 28, gasespass across a high pressure turbine 40, low pressure turbine 34, andfan/gear drive turbine 26.

A plurality of vanes and stators 50 may be mounted between the severalturbine sections. In particular, as shown, the low pressure compressor30 rotates with an intermediate pressure spool 32 and the low pressureturbine 34 in a first (“+”) direction. The fan drive turbine 26 rotateswith a shaft 25 in the same (“+”) direction as the low pressure spool32. The speed change gear 24 may cause the fan 22 to rotate in anopposed, second (“−”) direction. However, the fan rotating in the samedirection (the first direction) would come within the scope of thisinvention. As is known within the art and as illustrated, a star geararrangement may be utilized for the fan to rotate in an oppositedirection as to the fan/gear drive turbine 26. On the other hand, aplanetary gear arrangement may be utilized in the illustratedembodiment, wherein the two rotate in the same direction. The highpressure compressor 36 rotates with a spool 38 and is driven by a highpressure turbine 40 in the first direction (“+”).

Since the turbines 26, 34 and 40 are rotating in the same direction, afirst type of vane 50 is incorporated between these three sections. Vane50 may be a highly cambered vane, and may be used in combination with amid-turbine frame. The vane 50 may be incorporated into a mid-turbineframe as an air turning mid-turbine frame (“tmtf”) vane.

The fan drive turbine 26 in this arrangement can operate at a higherspeed than other fan drive turbine arrangements. The fan drive turbinecan have shrouded blades, which provides design freedom.

The low pressure compressor may have more than three stages. The fandrive turbine has at least two, and up to six stages. The high pressureturbine as illustrated may have one or two stages, and the low pressureturbine may have one or two stages.

The above features achieve a more compact turbine section volumerelative to the prior art, including both the high and low pressureturbines. A range of materials can be selected. As one example, byvarying the materials for forming the low pressure turbine, the volumecan be reduced through the use of more expensive and more exoticengineered materials, or alternatively, lower priced materials can beutilized. In three exemplary embodiments the first rotating blade of thefan drive turbine can be a directionally solidified casting blade, asingle crystal casting blade or a hollow, internally cooled blade. Allthree embodiments will change the turbine volume to be dramaticallysmaller than the prior art by increasing low pressure turbine speed.

Due to the compact turbine section, a power density, which may bedefined as thrust in pounds force produced divided by the volume of theentire turbine section, may be optimized. The volume of the turbinesection may be defined by an inlet of a first turbine vane in the highpressure turbine to the exit of the last rotating airfoil in thefan/gear drive turbine 26, and may be expressed in cubic inches. Thestatic thrust at the engine's flat rated Sea Level Takeoff conditiondivided by a turbine section volume is defined as power density. The sealevel take-off flat-rated static thrust may be defined in pounds force,while the volume may be the volume from the annular inlet of the firstturbine vane in the high pressure turbine to the annular exit of thedownstream end of the last rotor section in the fan drive turbine. Themaximum thrust may be sea level take-off thrust “SLTO thrust” which iscommonly defined as the flat-rated static thrust produced by theturbofan at sea-level.

The volume V of the turbine section may be best understood from FIG. 2.The high pressure turbine is illustrated at 40, the low pressure turbineat 34 and the fan drive turbine at 26. The volume V is illustrated bydashed line, and extends from an inner periphery I to an outer peripheryO. The inner periphery is somewhat defined by the flowpath of therotors, but also by the inner platform flow paths of vanes. The outerperiphery is defined by the stator vanes and outer air seal structuresalong the flowpath. The volume extends from a most upstream 400 end ofthe most upstream blade 410 in the high pressure turbine section 40,typically its leading edge, and to the most downstream edge 401 of thelast rotating airfoil 412 in the fan drive turbine section 26.Typically, this will be the trailing edge of that airfoil 412.Mid-turbine frames and valves as illustrated in FIG. 1 may be included.

The power density in the disclosed gas turbine engine is much higherthan in the prior art. Eight exemplary engines are shown below whichincorporate turbine sections and overall engine drive systems andarchitectures as set forth in this application, and can be found inTable I as follows:

TABLE 1 Thrust SLTO Turbine section Thrust/turbine section volume Engine(lbf) volume from the Inlet (lbf/in³) 1 17,000 3,859 4.41 2 23,300 5,3304.37 3 29,500 6,745 4.37 4 33,000 6,745 4.84 5 96,500 31,086 3.10 696,500 62,172 1.55 7 96,500 46,629 2.07 8 37,098 6,745 5.50

Thus, in embodiments, the power density would be greater than or equalto about 1.5 lbf/in³. More narrowly, the power density would be greaterthan or equal to about 2.0 lbf/in³.

Even more narrowly, the power density would be greater than or equal toabout 3.0 lbf/in³.

More narrowly, the power density is greater than or equal to about 4.0lbf/in³.

Also, in embodiments, the power density is less than or equal to about5.5 lbf/in³.

The engine 20 in one example is a high-bypass geared aircraft engine.The bypass ratio is the amount of air delivered into bypass path Bdivided by the amount of air into core path C. In a further example, theengine 20 bypass ratio is greater than about six (6), with an exampleembodiment being greater than ten (10), the geared architecture 24 is anepicyclic gear train, such as a planetary gear system or other gearsystem, with a gear reduction ratio of greater than about 2.3 and thefan/gear drive turbine section 26 has a pressure ratio that is greaterthan about 5. In one disclosed embodiment, the engine 20 bypass ratio isgreater than about ten (10:1), the fan diameter is significantly largerthan that of the low pressure compressor section 30, and the fan/geardrive turbine section 26 has a pressure ratio that is greater than about5:1. In some embodiments, the high pressure turbine section 40 may havetwo or fewer stages. In contrast, the fan/gear drive turbine section 26,in some embodiments, has between two and six stages. Further thefan/gear drive turbine section 26 pressure ratio is total pressuremeasured prior to inlet of fan/gear drive turbine section 26 as relatedto the total pressure at the outlet of the fan/gear drive turbinesection 26 prior to an exhaust nozzle. The geared architecture 24 may bean epicycle gear train, such as a planetary gear system or other gearsystem, with a gear reduction ratio of greater than about 2.5:1. Itshould be understood, however, that the above parameters are onlyexemplary of one embodiment of a geared architecture engine and that thepresent invention is applicable to other gas turbine engines includingdirect drive turbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, withthe engine at its best fuel consumption—also known as “bucket cruiseThrust Specific Fuel Consumption (“TSFC”). TSFC is the industry standardparameter of the rate of lbm of fuel being burned per hour divided bylbf of thrust the engine produces at that flight condition. “Low fanpressure ratio” is the ratio of total pressure across the fan bladealone, before the fan exit guide vanes. The low fan pressure ratio asdisclosed herein according to one non-limiting embodiment is less thanabout 1.45. “Low corrected fan tip speed” is the actual fan tip speed inft/sec divided by an industry standard temperature correction of [(RamAir Temperature deg R)/518.7)̂0.5]. The “Low corrected fan tip speed” asdisclosed herein according to one non-limiting embodiment is less thanabout 1150 ft/second. Further, the fan 22 may have 26 or fewer blades.

Engines made with the disclosed architecture, and including turbinesections as set forth in this application, and with modifications comingfrom the scope of the claims in this application, thus provide very highefficient operation, and increased fuel efficiency and lightweightrelative to their trust capability.

Although an embodiment of this invention has been disclosed, a worker ofordinary skill in this art would recognize that certain modificationswould come within the scope of this invention. For that reason, thefollowing claims should be studied to determine the true scope andcontent of this invention.

What is claimed is:
 1. A gas turbine engine comprising: a fan rotor, afirst compressor rotor and a second compressor rotor, said secondcompressor rotor for compressing air to a higher pressure than saidfirst compressor rotor; a first turbine rotor, said first turbine rotorconfigured to drive said second compressor rotor, and a second turbinerotor, said second turbine configured to drive said first compressorrotor; a fan drive turbine positioned downstream of said second turbinerotor, said fan drive turbine for driving said fan rotor through a gearreduction; and said first compressor rotor and said second turbine rotorconfigured to rotate as an intermediate speed spool, and said secondcompressor rotor and said first turbine rotor configured to rotatetogether as a high speed spool, with said high speed spool, saidintermediate speed spool, and said fan drive turbine configured torotate in the same first direction.
 2. The engine as set forth in claim1, wherein said fan rotor is driven by said gear reduction to rotate inan opposed second direction.
 3. The engine as set forth in claim 1,wherein a power density of the engine is greater than or equal to about1.5 lbs/in³, and less than or equal to about 5.5 lbf/in³.
 4. The engineas set forth in claim 3, wherein said power density is defined as aratio of thrust produced by said engine expressed in pounds force to avolume of a turbine section incorporating each of said first turbinerotor, said second turbine rotor and said fan drive turbine rotor,expressed in cubic inches.
 5. The engine as set forth in claim 4,wherein said ratio is greater than or equal to about 2.0.
 6. The engineas set forth in claim 5, wherein said ratio is greater than or equal toabout 4.0.
 7. The engine as set forth in claim 6, wherein said thrust issea level take-off flat-rated static thrust.
 8. The engine as set forthin claim 7, wherein said fan rotor is configured to deliver a portion ofair into a bypass duct and a portion of air into said first compressorrotor as core flow.
 9. The engine as set forth in claim 8, wherein amid-turbine frame is positioned between said first and second turbinerotors.
 10. The engine as set forth in claim 9, wherein a vane ispositioned between said mid-turbine frame and said second turbine rotor.11. The engine as set forth in claim 10, wherein a vane is positionedbetween said second turbine rotor and said fan drive turbine.
 12. Theengine as set forth in claim 8, wherein a vane is positioned betweensaid second turbine rotor and said fan drive turbine.
 13. The engine asset forth in claim 1, wherein a mid-turbine frame is positioned betweensaid first and second turbine rotors.
 14. The engine as set forth inclaim 13, wherein a vane is positioned between said mid-turbine frameand said second turbine rotor.
 15. The engine as set forth in claim 14,wherein a vane is positioned between said second turbine rotor and saidfan drive turbine.
 16. The engine as set forth in claim 1, wherein avane is positioned between said second turbine rotor and said fan driveturbine.
 17. A gas turbine engine comprising: a fan rotor, a firstcompressor rotor and a second compressor rotor, said second compressorrotor for compressing air to a higher pressure than said firstcompressor rotor; a first turbine rotor, said first turbine rotorconfigured to drive said second compressor rotor, and a second turbinerotor, said second turbine configured to drive said first compressorrotor; a fan drive turbine positioned downstream of said second turbinerotor, said fan drive turbine configured to drive said fan rotor througha gear reduction; said first compressor rotor and said second turbinerotor rotating as an intermediate speed spool, said second compressorrotor and said first turbine rotor rotating together as a high speedspool, with said high speed spool, said intermediate speed spool, andsaid fan drive turbine configured to rotate in the same direction; saidfan rotor being driven by said speed reduction to rotate in an opposedsecond direction; a power density of the engine being greater than orequal to about 1.5 lbf/in³, and less than or equal to about 5.5 lbf/in³;and said power density defined as a ratio of thrust produced by saidengine expressed in pounds force to a volume of a turbine sectionincorporating each of said first turbine rotor, said second turbinerotor and said fan drive turbine rotor, expressed in cubic inches. 18.The engine as set forth in claim 17, wherein said ratio is greater thanor equal to about 2.0.
 19. The engine as set forth in claim 18, whereinsaid ratio is greater than or equal to about 4.0.
 20. The engine as setforth in claim 19, wherein said thrust is sea level take-off flat-ratedstatic thrust.